Electrically variable transmission having three planetary gear sets and clutched motor/generators

ABSTRACT

The electrically variable transmission family of the present invention provides low-content, low-cost electrically variable transmission mechanisms including first, second and third differential gear sets, a battery, two electric machines serving interchangeably as motors or generators, up to five selectable torque-transfer devices and possibly a dog clutch. The selectable torque transmitting devices are engaged to yield an EVT with a continuously variable range of speeds (including reverse) and four mechanically fixed forward speed ratios. The torque transmitting devices and the first and second motor/generators are operable to provide five operating modes in the electrically variable transmission, including battery reverse mode, EVT reverse mode, reverse and forward launch modes, continuously variable transmission range mode, and fixed ratio mode.

TECHNICAL FIELD

The present invention relates to electrically variable transmissionswith selective operation both in power-split variable speed ratio rangesand in fixed speed ratios, and having three planetary gear sets, twomotor/generators and up to five torque transmitting devices.

BACKGROUND OF THE INVENTION

Internal combustion engines, particularly those of the reciprocatingpiston type, currently propel most vehicles. Such engines are relativelyefficient, compact, lightweight, and inexpensive mechanisms by which toconvert highly concentrated energy in the form of fuel into usefulmechanical power. A novel transmission system, which can be used withinternal combustion engines and which can reduce fuel consumption andthe emissions of pollutants, may be of great benefit to the public.

The wide variation in the demands that vehicles typically place oninternal combustion engines increases fuel consumption and emissionsbeyond the ideal case for such engines. Typically, a vehicle ispropelled by such an engine, which is started from a cold state by asmall electric motor and relatively small electric storage batteries,then quickly placed under the loads from propulsion and accessoryequipment. Such an engine is also operated through a wide range ofspeeds and a wide range of loads and typically at an average ofapproximately a fifth of its maximum power output.

A vehicle transmission typically delivers mechanical power from anengine to the remainder of a drive system, such as fixed final drivegearing, axles and wheels. A typical mechanical transmission allows somefreedom in engine operation, usually through alternate selection of fiveor six different drive ratios, a neutral selection that allows theengine to operate accessories with the vehicle stationary, and clutchesor a torque converter for smooth transitions between driving ratios andto start the vehicle from rest with the engine turning. Transmissiongear selection typically allows power from the engine to be delivered tothe rest of the drive system with a ratio of torque multiplication andspeed reduction, with a ratio of torque reduction and speedmultiplication known as overdrive, or with a reverse ratio.

An electric generator can transform mechanical power from the engineinto electrical power, and an electric motor can transform that electricpower back into mechanical power at different torques and speeds for theremainder of the vehicle drive system. This arrangement allows acontinuous variation in the ratio of torque and speed between engine andthe remainder of the drive system, within the limits of the electricmachinery. An electric storage battery used as a source of power forpropulsion may be added to this arrangement, forming a series hybridelectric drive system.

The series hybrid system allows the engine to operate with someindependence from the torque, speed and power required to propel avehicle, so the engine may be controlled for improved emissions andefficiency. This system allows the electric machine attached to theengine to act as a motor to start the engine. This system also allowsthe electric machine attached to the remainder of the drive train to actas a generator, recovering energy from slowing the vehicle into thebattery by regenerative braking. A series electric drive suffers fromthe weight and cost of sufficient electric machinery to transform all ofthe engine power from mechanical to electrical in the generator and fromelectrical to mechanical in the drive motor, and from the useful energylost in these conversions.

A power-split transmission can use what is commonly understood to be“differential gearing” to achieve a continuously variable torque andspeed ratio between input and output. An electrically variabletransmission can use differential gearing to send a fraction of itstransmitted power through a pair of electric motor/generators. Theremainder of its power flows through another, parallel path that is allmechanical and direct, of fixed ratio, or alternatively selectable.

One form of differential gearing, as is well known to those skilled inthis art, may constitute a planetary gear set. Planetary gearing isusually the preferred embodiment employed in differentially gearedinventions, with the advantages of compactness and different torque andspeed ratios among all members of the planetary gear set. However, it ispossible to construct this invention without planetary gears, as byusing bevel gears or other gears in an arrangement where the rotationalspeed of at least one element of a gear set is always a weighted averageof speeds of two other elements.

A hybrid electric vehicle transmission system also includes one or moreelectric energy storage devices. The typical device is a chemicalelectric storage battery, but capacitive or mechanical devices, such asan electrically driven flywheel, may also be included. Electric energystorage allows the mechanical output power from the transmission systemto the vehicle to vary from the mechanical input power from the engineto the transmission system. The battery or other device also allows forengine starting with the transmission system and for regenerativevehicle braking.

An electrically variable transmission in a vehicle can simply transmitmechanical power from an engine input to a final drive output. To do so,the electric power produced by one motor/generator balances theelectrical losses and the electric power consumed by the othermotor/generator. By using the above-referenced electrical storagebattery, the electric power generated by one motor/generator can begreater than or less than the electric power consumed by the other.Electric power from the battery can sometimes allow bothmotor/generators to act as motors, especially to assist the engine withvehicle acceleration. Both motors can sometimes act as generators torecharge the battery, especially in regenerative vehicle braking.

A successful substitute for the series hybrid transmission is thetwo-range, input-split and compound-split electrically variabletransmission now produced for transit buses, as disclosed in U.S. Pat.No. 5,931,757, issued Aug. 3, 1999, to Michael Roland Schmidt, commonlyassigned with the present application, and hereby incorporated byreference in its entirety. Such a transmission utilizes an input meansto receive power from the vehicle engine and a power output means todeliver power to drive the vehicle. First and second motor/generatorsare connected to an energy storage device, such as a battery, so thatthe energy storage device can accept power from, and supply power to,the first and second motor/generators. A control unit regulates powerflow among the energy storage device and the motor/generators as well asbetween the first and second motor/generators.

Operation in first or second variable-speed-ratio modes of operation maybe selectively achieved by using clutches in the nature of first andsecond torque transfer devices. In the first mode, an input-power-splitspeed ratio range is formed by the application of the first clutch, andthe output speed of the transmission is proportional to the speed of onemotor/generator. In the second mode, a compound-power-split speed ratiorange is formed by the application of the second clutch, and the outputspeed of the transmission is not proportional to the speeds of either ofthe motor/generators, but is an algebraic linear combination of thespeeds of the two motor/generators. Operation at a fixed transmissionspeed ratio may be selectively achieved by the application of both ofthe clutches. Operation of the transmission in a neutral mode may beselectively achieved by releasing both clutches, decoupling the engineand both electric motor/generators from the transmission output. Thetransmission incorporates at least one mechanical point in its firstmode of operation and at least two mechanical points in its second modeof operation.

“Compound split” means that neither the transmission input nor output isdirectly connected to a motor/generator. A compound split architectureincludes a mode with two mechanical points, each of which is attainedwhen one of the motor/generators reaches zero speed. This allows areduction in the size and cost of the electric motor/generator requiredto achieve desired vehicle performance. “Output split” means amotor/generator is directly connected to the input. This mode is usefulfor launching the vehicle. “Input split” means a motor/generator isdirectly connected to the output member. This is useful in capturingregenerative energy during braking and for providing torque assist tothe engine as needed.

U.S. Pat. No. 6,527,658, issued Mar. 4, 2003 to Holmes et al, commonlyassigned with the present application, and hereby incorporated byreference in its entirety, discloses an electrically variabletransmission utilizing two planetary gear sets, two motor/generators andtwo clutches to provide input split, compound split, neutral and reversemodes of operation. Both planetary gear sets may be simple, or one maybe individually compounded. An electrical control member regulates powerflow among an energy storage device and the two motor/generators. Thistransmission provides two ranges or modes of electrically variabletransmission (EVT) operation, selectively providing an input-power-splitspeed ratio range and a compound-power-split speed ratio range. Onefixed speed ratio can also be selectively achieved.

SUMMARY OF THE INVENTION

The present invention provides a family of electrically variabletransmissions offering several advantages over conventional automatictransmissions for use in hybrid vehicles, including improved vehicleacceleration performance, improved fuel economy via regenerative brakingand electric-only idling and launch, and an attractive marketingfeature. An object of the invention is to provide the best possibleenergy efficiency and emissions for a given engine. In addition, optimalperformance, capacity, package size, and ratio coverage for thetransmission are sought.

The electrically variable transmission family of the present inventionprovides low-content, low-cost electrically variable transmissionmechanisms including first, second and third differential gear sets, abattery, two electric machines serving interchangeably as motors orgenerators, and three, four or five selectable torque-transmittingdevices. Additionally, a dog clutch may be provided. Preferably, thedifferential gear sets are planetary gear sets, such as simple orcompound (including Ravigneaux) gear sets, but other gear arrangementsmay be implemented, such as bevel gears or differential gearing to anoffset axis.

In this description, the first, second, or third gear sets may becounted first to third in any order (i.e., left to right, right to left,etc.).

Each of the three gear sets has three members. The first, second orthird member of each gear set can be any one of a sun gear, ring gear orcarrier member, or alternatively a pinion. A fourth member may also beprovided, such as a secondary sun gear driven by a long pinion.

Each carrier member can be either a single-pinion carrier member(simple) or a double-pinion carrier member (compound).

The input shaft is continuously connected with at least one member ofthe gear sets. The output shaft is continuously connected with anothermember of the gear sets.

A first interconnecting member continuously connects the first member ofthe first gear set with the first member of the second gear set.

A second interconnecting member continuously connects the first memberof the third gear set with the second or third member of the first gearset or with a stationary member (transmission housing/casing).

A third interconnecting member continuously connects a second member ofthe first gear set with the second member of the second or third gearset.

A first torque transmitting device selectively connects a member of thefirst gear set with another member of the first, second or third gearset.

A second torque transmitting device selectively connects a member of thethird gear set with a member of the first or second gear set.

An optional third torque transmitting device selectively connects amember of the third gear set with a stationary member(ground/transmission case).

A fourth (or third) torque transmitting device is connected in parallelwith one of the motor/generators for selectively preventing rotation ofthe motor/generator.

An optional fifth (or fourth) torque transmitting device is connected inparallel with the other of the motor/generators for selectivelypreventing rotation thereof.

The first motor/generator is mounted to the transmission case (orground) and is continuously connected to a member of the first or secondgear set. The first motor/generator connection may incorporate offsetgearing.

The second motor/generator is mounted to the transmission case and isselectively connected via a dog clutch to one of a pair of members ofthe first, second or third gear sets. The second motor/generator mayalso incorporate offset gearing. The dog clutch may reduce clutch spinlosses, and allows motor/generator operation at low speeds throughoutthe operating range of the transmission. The dog clutch may be replacedby a pair of conventional torque transfer devices.

The selectable torque transmitting devices are engaged in combinationsto yield an EVT with a continuously variable range of speeds (includingreverse) and four mechanically fixed forward speed ratios. A “fixedspeed ratio” is an operating condition in which the mechanical powerinput to the transmission is transmitted mechanically to the output, andno power flow (i.e. almost zero) is present in the motor/generators. Anelectrically variable transmission that may selectively achieve severalfixed speed ratios for operation near full engine power can be smallerand lighter for a given maximum capacity. Fixed ratio operation may alsoresult in lower fuel consumption when operating under conditions whereengine speed can approach its optimum without using themotor/generators. A variety of fixed speed ratios and variable ratiospreads can be realized by suitably selecting the tooth ratios of thegear sets.

Each embodiment of the electrically variable transmission familydisclosed has an architecture in which neither the transmission inputnor output is directly connected to a motor/generator. This allows for areduction in the size and cost of the electric motor/generators requiredto achieve the desired vehicle performance.

The torque transmitting devices, and the first and secondmotor/generators are operable to provide five operating modes in theelectrically variable transmission, including battery reverse mode, EVTreverse mode, reverse and forward launch modes, continuously variabletransmission range mode, and fixed ratio mode.

The above features and advantages, and other features and advantages ofthe present invention are readily apparent from the following detaileddescription of the best modes for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a schematic representation of a powertrain including anelectrically variable transmission incorporating a family member of thepresent invention;

FIG. 1 b is an operating mode table and fixed ratio mode table depictingsome of the operating characteristics of the powertrain shown in FIG. 1a;

FIG. 2 a is a schematic representation of a powertrain having anelectrically variable transmission incorporating another family memberof the present invention;

FIG. 2 b is an operating mode table and fixed ratio mode table depictingsome of the operating characteristics of the powertrain shown in FIG. 2a;

FIG. 3 a is a schematic representation of a powertrain having anelectrically variable transmission incorporating another family memberof the present invention;

FIG. 3 b is an operating mode table and fixed ratio mode table depictingsome of the operating characteristics of the powertrain shown in FIG. 3a;

FIG. 4 a is a schematic representation of a powertrain having anelectrically variable transmission incorporating another family memberof the present invention;

FIG. 4 b is an operating mode table and fixed ratio mode table depictingsome of the operating characteristics of the powertrain shown in FIG. 4a;

FIG. 5 a is a schematic representation of a powertrain having anelectrically variable transmission incorporating another family memberof the present invention; and

FIG. 5 b is an operating mode table and fixed ratio mode table depictingsome of the operating characteristics of the powertrain shown in FIG. 5a.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 1 a, a powertrain 10 is shown, including anengine 12 connected to one preferred embodiment of the improvedelectrically variable transmission (EVT), designated generally by thenumeral 14. Transmission 14 is designed to receive at least a portion ofits driving power from the engine 12. As shown, the engine 12 has anoutput shaft that serves as the input member 17 of the transmission 14.A transient torque damper (not shown) may also be implemented betweenthe engine 12 and the input member 17 of the transmission.

In the embodiment depicted the engine 12 may be a fossil fuel engine,such as a diesel engine which is readily adapted to provide itsavailable power output typically delivered at a constant number ofrevolutions per minute (RPM).

Irrespective of the means by which the engine 12 is connected to thetransmission input member 17, the transmission input member 17 isoperatively connected to a planetary gear set in the transmission 14. Anoutput member 19 of the transmission 14 is connected to a final drive16.

The transmission 14 utilizes three differential gear sets, preferably inthe nature of planetary gear sets 20, 30 and 40. The planetary gear set20 employs an outer gear member 24, typically designated as the ringgear. The ring gear member 24 circumscribes an inner gear member 22,typically designated as the sun gear. A carrier member 26 rotatablysupports a plurality of planet gears 27 such that each planet gear 27meshingly engages both the outer, ring gear member 24 and the inner, sungear member 22 of the first planetary gear set 20.

The planetary gear set 30 also has an outer gear member 34, often alsodesignated as the ring gear, that circumscribes an inner gear member 32,also often designated as the sun gear member. A plurality of planetgears 37 are also rotatably mounted in a carrier member 36 such thateach planet gear member 37 simultaneously, and meshingly, engages boththe outer, ring gear member 34 and the inner, sun gear member 32 of theplanetary gear set 30.

The planetary gear set 40 also has an outer gear member 44, often alsodesignated as the ring gear, that circumscribes an inner gear member 42,also often designated as the sun gear. A plurality of planet gears 47are also rotatably mounted in a carrier member 46 such that each planetgear member 47 simultaneously, and meshingly, engages both the outer,ring gear member 44 and the inner, sun gear member 42 of the planetarygear set 40.

A first interconnecting member 70 continuously connects the carriermember 26 of the planetary gear set 20 with the carrier member 36 of theplanetary gear set 30. A second interconnecting member 72 continuouslyconnects the sun gear member 32 of the planetary gear set 30 with thesun gear member 42 of the planetary gear set 40. A third interconnectingmember 74 continuously connects the sun gear member 22 of the planetarygear set 20 with the ring gear member 34 of the planetary gear set 30.

The first preferred embodiment 10 also incorporates first and secondmotor/generators 80 and 82, respectively. The stator of the firstmotor/generator 80 is secured to the transmission housing 60. The rotorof the first motor/generator 80 is secured to the ring gear member 34 ofthe planetary gear set 30.

The stator of the second motor/generator 82 is also secured to thetransmission housing 60. The rotor of the second motor/generator 82 isselectively connectable to the sun gear member 42 or the carrier member46 of the planetary gear set 40 via the dog clutch 92 alternatingbetween positions “A” and “B”. The rotor of the second motor/generator82 is connected to the dog clutch 92 via offset gearing 90. The dogclutch may be replaced by a pair of clutches as is understood by thoseskilled in the art.

A first torque transmitting device, such as clutch 50, selectivelyconnects the carrier member 26 of the planetary gear set 20 with thering gear member 24 of the planetary gear set 20. A second torquetransmitting device, such as clutch 52, selectively connects the ringgear member 34 of the planetary gear set 30 with the ring gear member 44of the planetary gear set 40. A third torque transmitting device, suchas brake 54, selectively connects the ring gear member 44 with thetransmission housing 60. A fourth torque transmitting device, such asbrake 57, is connected in parallel with the motor/generator 82 forselectively braking rotation thereof. The first, second, third, andfourth torque transmitting devices 50, 52, 54 and 57 are employed toassist in the selection of the operational modes of the hybridtransmission 14, as will be hereinafter more fully explained.

The input drive member 17 is secured to the ring gear member 24 of theplanetary gear set 20. The output drive member 19 of the transmission 14is secured to carrier member 46 of the planetary gear set 40.

Returning now to the description of the power sources, it should beapparent from the foregoing description, and with particular referenceto FIG. 1 a, that the transmission 14 selectively receives power fromthe engine 12. The hybrid transmission also receives power from anelectric power source 86, which is operably connected to a controller88. The electric power source 86 may be one or more batteries. Otherelectric power sources, such as fuel cells, that have the ability toprovide, or store, and dispense electric power may be used in place ofbatteries without altering the concepts of the present invention.

General Operating Considerations

One of the primary control devices is a well known drive range selector(not shown) that directs an electronic control unit (the ECU 88) toconfigure the transmission for either the park, reverse, neutral, orforward drive range. The second and third primary control devicesconstitute an accelerator pedal (not shown) and a brake pedal (also notshown). The information obtained by the ECU from these three primarycontrol sources is designated as the “operator demand.” The ECU alsoobtains information from a plurality of sensors (input as well asoutput) as to the status of: the torque transfer devices (either appliedor released); the engine output torque; the unified battery, orbatteries, capacity level; and, the temperatures of selected vehicularcomponents. The ECU determines what is required and then manipulates theselectively operated components of, or associated with, the transmissionappropriately to respond to the operator demand.

The invention may use simple or compound planetary gear sets. In asimple planetary gear set a single set of planet gears are normallysupported for rotation on a carrier member that is itself rotatable.

In a simple planetary gear set, when the sun gear is held stationary andpower is applied to the ring gear of a simple planetary gear set, theplanet gears rotate in response to the power applied to the ring gearand thus “walk” circumferentially about the fixed sun gear to effectrotation of the carrier member in the same direction as the direction inwhich the ring gear is being rotated.

When any two members of a simple planetary gear set rotate in the samedirection and at the same speed, the third member is forced to turn atthe same speed, and in the same direction. For example, when the sungear and the ring gear rotate in the same direction, and at the samespeed, the planet gears do not rotate about their own axes but ratheract as wedges to lock the entire unit together to effect what is knownas direct drive. That is, the carrier member rotates with the sun andring gears.

However, when the two gear members rotate in the same direction, but atdifferent speeds, the direction in which the third gear member rotatesmay often be determined simply by visual analysis, but in manysituations the direction will not be obvious and can only be accuratelydetermined by knowing the number of teeth present on all the gearmembers of the planetary gear set.

Whenever the carrier member is restrained from spinning freely, andpower is applied to either the sun gear or the ring gear, the planetgear members act as idlers. In that way the driven member is rotated inthe opposite direction as the drive member. Thus, in many transmissionarrangements when the reverse drive range is selected, a torque transferdevice serving as a brake is actuated frictionally to engage the carriermember and thereby restrain it against rotation so that power applied tothe sun gear will turn the ring gear in the opposite direction. Thus, ifthe ring gear is operatively connected to the drive wheels of a vehicle,such an arrangement is capable of reversing the rotational direction ofthe drive wheels, and thereby reversing the direction of the vehicleitself.

In a simple set of planetary gears, if any two rotational speeds of thesun gear, the planet carrier member, and the ring gear are known, thenthe speed of the third member can be determined using a simple rule. Therotational speed of the carrier member is always proportional to thespeeds of the sun and the ring, weighted by their respective numbers ofteeth. For example, a ring gear may have twice as many teeth as the sungear in the same set. The speed of the carrier member is then the sum oftwo-thirds the speed of the ring gear and one-third the speed of the sungear. If one of these three members rotates in an opposite direction,the arithmetic sign is negative for the speed of that member inmathematical calculations.

The torque on the sun gear, the carrier member, and the ring gear canalso be simply related to one another if this is done withoutconsideration of the masses of the gears, the acceleration of the gears,or friction within the gear set, all of which have a relatively minorinfluence in a well designed transmission. The torque applied to the sungear of a simple planetary gear set must balance the torque applied tothe ring gear, in proportion to the number of teeth on each of thesegears. For example, the torque applied to a ring gear with twice as manyteeth as the sun gear in that set must be twice that applied to the sungear, and must be applied in the same direction. The torque applied tothe carrier member must be equal in magnitude and opposite in directionto the sum of the torque on the sun gear and the torque on the ringgear.

In a compound planetary gear set, the utilization of inner and outersets of planet gears effects an exchange in the roles of the ring gearand the planet carrier member in comparison to a simple planetary gearset. For instance, if the sun gear is held stationary, the planetcarrier member will rotate in the same direction as the ring gear, butthe planet carrier member with inner and outer sets of planet gears willtravel faster than the ring gear, rather than slower.

In a compound planetary gear set having meshing inner and outer sets ofplanet gears the speed of the ring gear is proportional to the speeds ofthe sun gear and the planet carrier member, weighted by the number ofteeth on the sun gear and the number of teeth filled by the planetgears, respectively. For example, the difference between the ring andthe sun filled by the planet gears might be as many teeth as are on thesun gear in the same set. In that situation the speed of the ring gearwould be the sum of two-thirds the speed of the carrier member and onethird the speed of the sun. If the sun gear or the planet carrier memberrotates in an opposite direction, the arithmetic sign is negative forthat speed in mathematical calculations.

If the sun gear were to be held stationary, then a carrier member withinner and outer sets of planet gears will turn in the same direction asthe rotating ring gear of that set. On the other hand, if the sun gearwere to be held stationary and the carrier member were to be driven,then planet gears in the inner set that engage the sun gear roll, or“walk,” along the sun gear, turning in the same direction that thecarrier member is rotating. Pinion gears in the outer set that mesh withpinion gears in the inner set will turn in the opposite direction, thusforcing a meshing ring gear in the opposite direction, but only withrespect to the planet gears with which the ring gear is meshinglyengaged. The planet gears in the outer set are being carried along inthe direction of the carrier member. The effect of the rotation of thepinion gears in the outer set on their own axis and the greater effectof the orbital motion of the planet gears in the outer set due to themotion of the carrier member are combined, so the ring rotates in thesame direction as the carrier member, but not as fast as the carriermember.

If the carrier member in such a compound planetary gear set were to beheld stationary and the sun gear were to be rotated, then the ring gearwill rotate with less speed and in the same direction as the sun gear.If the ring gear of a simple planetary gear set is held stationary andthe sun gear is rotated, then the carrier member supporting a single setof planet gears will rotate with less speed and in the same direction asthe sun gear. Thus, one can readily observe the exchange in rolesbetween the carrier member and the ring gear that is caused by the useof inner and outer sets of planet gears which mesh with one another, incomparison with the usage of a single set of planet gears in a simpleplanetary gear set.

The normal action of an electrically variable transmission is totransmit mechanical power from the input to the output. As part of thistransmission action, one of its two motor/generators acts as a generatorof electrical power. The other motor/generator acts as a motor and usesthat electrical power. As the speed of the output increases from zero toa high speed, the two motor/generators 80, 82 gradually exchange rolesas generator and motor, and may do so more than once. These exchangestake place around mechanical points, where essentially all of the powerfrom input to output is transmitted mechanically and no substantialpower is transmitted electrically.

In a hybrid electrically variable transmission system, the battery 86may also supply power to the transmission or the transmission may supplypower to the battery. If the battery is supplying substantial electricpower to the transmission, such as for vehicle acceleration, then bothmotor/generators may act as motors. If the transmission is supplyingelectric power to the battery, such as for regenerative braking, bothmotor/generators may act as generators. Very near the mechanical pointsof operation, both motor/generators may also act as generators withsmall electrical power outputs, because of the electrical losses in thesystem.

Contrary to the normal action of the transmission, the transmission mayactually be used to transmit mechanical power from the output to theinput. This may be done in a vehicle to supplement the vehicle brakesand to enhance or to supplement regenerative braking of the vehicle,especially on long downward grades. If the power flow through thetransmission is reversed in this way, the roles of the motor/generatorswill then be reversed from those in normal action.

Specific Operating Considerations

Each of the embodiments described herein has sixteen functionalrequirements (corresponding with the 16 rows of each operating modetable shown in the Figures) which may be grouped into five operatingmodes. These five operating modes are described below and may be bestunderstood by referring to the respective operating mode tableaccompanying each transmission stick diagram, such as the operating modetables of FIGS. 1 b, 2 b, 3 b, etc.

The first operating mode is the “battery reverse mode” which correspondswith the first row (Batt Rev) of each operating mode table, such as thatof FIG. 1 b. In this mode, the engine is off and the transmissionelement connected to the engine is not controlled by engine torque,though there may be some residual torque due to the rotational inertiaof the engine. The EVT is driven by one of the motor/generators usingenergy from the battery, causing the vehicle to move in reverse.Depending on the kinematic configuration, the other motor/generator mayor may not rotate in this mode, and may or may not transmit torque. Ifit does rotate, it is used to generate energy which is stored in thebattery. In the embodiment of FIG. 1 b, in the battery reverse mode, thebrake 54 is engaged and the dog clutch 92 is in position A, thegenerator 80 has zero torque, the motor 82 has a torque of −1.00, and atorque ratio of −3.25 is achieved, by way of example. In each operatingmode table an (M) next to a torque value in the motor/generator columns80 and 82 indicates that the motor/generator is acting as a motor, andthe absence of an (M) indicates that the motor/generator is acting asgenerator.

The second operating mode is the “EVT reverse mode” (or mechanicalreverse mode) which corresponds with the second row (EVT Rev) of eachoperating mode table, such as that of FIG. 1 b. In this mode, the EVT isdriven by the engine and by one of the motor/generators. The othermotor/generator operates in generator mode and transfers 100% of thegenerated energy back to the driving motor. The net effect is to drivethe vehicle in reverse. Referring to FIG. 1 b, for example, in the EVTreverse mode, the brake 54 is engaged and the dog clutch 92 is inposition A, the generator 80 has a torque of −0.39 units, the motor 82has a torque of −3.17 units, and an output torque of −8.33 is achieved,corresponding to an engine torque of 1 unit.

The third operating mode includes the “reverse and forward launch modes”(also referred to as “torque converter reverse and forward modes”)corresponding with the third and fourth rows (TC Rev and TC For) of eachoperating mode table, such as that of FIG. 1 b. In this mode, the EVT isdriven by the engine and one of the motor/generators. A selectablefraction of the energy generated in the generator unit is stored in thebattery, with the remaining energy being transferred to the motor. InFIG. 1, this fraction is approximately 99%. The ratio of transmissionoutput speed to engine speed (transmission speed ratio) is approximately+/−0.001 (the positive sign indicates that the vehicle is creepingforward and negative sign indicates that the vehicle is creepingbackwards). Referring to FIG. 1 b, in the TC Reverse mode, the brake 54is engaged and the dog clutch 92 is in position A, the motor/generator80 acts as a generator with −0.51 units of torque, the motor/generator82 acts as a motor with −2.84 units of torque, and a torque ratio of−7.00 is achieved. In the TC Forward mode, the brake 54 is engaged andthe dog clutch 92 is in position A, the motor/generator 80 acts as agenerator with −0.39 units of torque, the motor/generator 82 acts as amotor with 0.83 units of torque, and a torque ratio of 4.69 is achieved.

The fourth operating mode is a “continuously variable transmission rangemode” which includes the Range 1.1, Range 1.2, Range 1.3, Range 1.4,Range 2.1, Range 3.1, Range 3.2 and Range 3.3 operating pointscorresponding with rows 5-12 of each operating point table, such as thatof FIG. 1 b. In this mode, the EVT is driven by the engine as well asone of the motor/generators operating as a motor. The othermotor/generator operates as a generator and transfers 100% of thegenerated energy back to the motor. The operating points represented byRange 1.1, 1.2, . . . , etc. are discrete points in the continuum offorward speed ratios provided by the EVT. For example in FIG. 1 b, arange of torque ratios from 4.69 to 1.86 is achieved with the brake 54engaged and the dog clutch 92 in position A. A torque ratio of 1.36 isachieved with the clutch 52 engaged and the dog clutch 92 in position A.A range of torque ratios from 1.00 to 0.54 is achieved with the clutch52 engaged and the dog clutch 92 in position B.

The fifth operating mode includes the “fixed ratio” modes (F1, F2, F3and F4) corresponding with rows 13-16 of each operating mode table (i.e.operating mode table), such as that of FIG. 1 b. In this mode thetransmission operates like a conventional automatic transmission, withone torque transmitting device engaged to create a discrete transmissionratio. The clutching table accompanying each figure shows only threefixed-ratio forward speeds but additional fixed ratios may be available.Referring to FIG. 1 b, in fixed ratio F1 the clutch 52 and brake 54 areengaged and the dog clutch 92 is in position A to achieve a fixed torqueratio of 3.26. In fixed ratio F2, the clutch 52 and brake 54 are engagedand the dog clutch 92 is in position A to achieve a fixed ratio of 2.00.In fixed ratio F3, the clutches 50 and 52 are engaged and the dog clutch92 is in position A to achieve a fixed ratio of 1.00. In fixed ratio F4,the clutch 52 and brake 57 are engaged and the dog clutch 92 is inposition A to achieve a fixed ratio of 0.56. Accordingly, each “X” inthe column of motor/generator 82 in FIG. 1 b indicates that the brake 57is engaged, respectively, and the motor/generator 82 is not rotating.

The powertrain 10 may also operate in a “charge-depleting mode”. Forpurposes of the present invention, a “charge-depleting mode” is a modewherein the vehicle is powered primarily by an electric motor/generatorsuch that the battery 86 is depleted or nearly depleted when the vehiclereaches its destination. In other words, during the charge-depletingmode, the engine 12 is only operated to the extent necessary to ensurethat the battery 86 is not depleted before the destination is reached. Aconventional hybrid vehicle operates in a “charge-sustaining mode”,wherein if the battery charge level drops below a predetermined level(e.g., 25%) the engine is automatically run to recharge the battery.Therefore, by operating in a charge-depleting mode, the hybrid vehiclecan conserve some or all of the fuel that would otherwise be expended tomaintain the 25% battery charge level in a conventional hybrid vehicle.It should be appreciated that the vehicle powertrain is preferably onlyoperated in the charge-depleting mode if the battery 86 can be rechargedafter the destination is reached by plugging it into an energy source(not shown).

Also, the engine 12 may be powered using various types of fuel toimprove the efficiency and fuel economy of a particular application.Such fuels may include, for example, gasoline; diesel; ethanol; dimethylether; etc.

The transmission 14 is capable of operating in so-called single ormultiple modes. In single mode, the engaged torque transmitting deviceremains the same for the entire continuum of forward speed ratios(represented by the discrete points: Ranges 1.1, 1.2, 1.3 and 1.4). Indual-, three-, four- etc. modes, the engaged torque transmitting deviceis switched at some intermediate speed ratios (e.g., Range 2.1 and 3.1in FIG. 1). Depending on the mechanical configuration, this change intorque transmitting device engagement has advantages in reducing elementspeeds in the transmission.

As set forth above, the engagement schedule for the torque transmittingdevices is shown in the operating mode table and fixed ratio mode tableof FIG. 1 b. FIG. 1 b also provides an example of torque ratios that areavailable utilizing the ring gear/sun gear tooth ratios given by way ofexample in FIG. 1 b. The N_(R1)/N_(S1) value is the tooth ratio of theplanetary gear set 20; the N_(R2)/N_(S2) value is the tooth ratio of theplanetary gear set 30; and the N_(R3)/N_(S3) value is the tooth ratio ofthe planetary gear set 40. Also, the chart of FIG. 1 b describes theratio steps that are attained utilizing the sample of tooth ratiosgiven. For example, the step ratio between first and second fixedforward torque ratios is 1.63, the step ratio between the second andthird fixed forward torque ratios is 2.00, the step ratio between thethird and fourth fixed forward torque ratios is 1.79 and the ratiospread is 5.82.

Description of a Second Exemplary Embodiment

With reference to FIG. 2 a, a powertrain 110 is shown, including anengine 12 connected to another embodiment of the improved electricallyvariable transmission, designated generally by the numeral 114.Transmission 114 is designed to receive at least a portion of itsdriving power from the engine 12.

In the embodiment depicted the engine 12 may also be a fossil fuelengine, such as a diesel engine which is readily adapted to provide itsavailable power output typically delivered at a constant number ofrevolutions per minute (RPM). As shown, the engine 12 has an outputshaft that serves as the input member 17 of the transmission 14. Atransient torque damper (not shown) may also be implemented between theengine 12 and the input member 17 of the transmission.

Irrespective of the means by which the engine 12 is connected to thetransmission input member 17, the transmission input member 17 isoperatively connected to a planetary gear set in the transmission 114.An output member 19 of the transmission 114 is connected to a finaldrive 16.

The transmission 114 utilizes three differential gear sets, preferablyin the nature of planetary gear sets 120, 130 and 140. The planetarygear set 120 employs an outer gear member 124, typically designated asthe ring gear. The ring gear member 124 circumscribes an inner gearmember 122, typically designated as the sun gear. A carrier member 126rotatably supports a plurality of planet gears 127 such that each planetgear 127 meshingly engages both the outer, ring gear member 124 and theinner, sun gear member 122 of the first planetary gear set 120.

The planetary gear set 130 also has an outer gear member 134, often alsodesignated as the ring gear, that circumscribes an inner gear member132, also often designated as the sun gear. A plurality of planet gears137 are also rotatably mounted in a carrier member 136 such that eachplanet gear member 137 simultaneously, and meshingly, engages both theouter, ring gear member 134 and the inner, sun gear member 132 of theplanetary gear set 130.

The planetary gear set 140 also has an outer gear member 144, often alsodesignated as the ring gear, that circumscribes an inner gear member142, also often designated as the sun gear. A plurality of planet gears147 are also rotatably mounted in a carrier member 146 such that eachplanet gear member 147 simultaneously, and meshingly, engages both theouter, ring gear member 144 and the inner, sun gear member 142 of theplanetary gear set 140.

The transmission input member 17 is connected to the carrier member 146of the planetary gear set 140. The transmission output member 19 isconnected with the carrier member 126 of the planetary gear set 120. Afirst interconnecting member 170 continuously connects the ring gearmember 124 of the planetary gear set 120 with the sun gear member 132 ofthe planetary gear set 130. A second interconnecting member 172continuously connects the sun gear member 142 of the planetary gear set140 with the transmission housing 160. A third interconnecting member174 continuously connects the carrier member 126 of the planetary gearset 120 with the carrier member 136 of the planetary gear set 130.

The transmission 114 also incorporates first and second motor/generators180 and 182, respectively. The stator of the first motor/generator 180is secured to the transmission housing 160. The rotor of the firstmotor/generator 180 is secured to the ring gear member 124 of theplanetary gear set 120.

The stator of the second motor/generator 182 is also secured to thetransmission housing 160. The rotor of the second motor/generator 182 isselectively connectable to the carrier member 126 or the sun gear member122 of the planetary gear set 120 via the dog clutch 192 alternatingbetween positions “A” and “B”. The rotor of the second motor/generator182 is connected to the dog clutch 192 via offset gearing 190. The dogclutch may be replaced by a pair of clutches as is understood by thoseskilled in the art.

A first torque transmitting device, such as clutch 150, selectivelyconnects the sun gear member 122 of the planetary gear set 120 with thering gear member 144 of the planetary gear set 140. A second torquetransmitting device, such as clutch 152, selectively connects the ringgear member 134 of the planetary gear set 130 with the carrier member146 of the planetary gear set 140. A third torque transmitting device,such as the brake 155, is connected in parallel with the motor/generator180 for selectively braking rotation thereof. A fourth torquetransmitting device, such as brake 157, is connected in parallel withthe motor/generator 182 for selectively braking rotation thereof. Thefirst, second, third and fourth torque transmitting devices 150, 152,155 and 157 are employed to assist in the selection of the operationalmodes of the hybrid transmission 114.

Returning now to the description of the power sources, it should beapparent from the foregoing description, and with particular referenceto FIG. 2 a, that the transmission 114 selectively receives power fromthe engine 12. The hybrid transmission also exchanges power with anelectric power source 186, which is operably connected to a controller188. The electric power source 186 may be one or more batteries. Otherelectric power sources, such as fuel cells, that have the ability toprovide, or store, and dispense electric power may be used in place ofbatteries without altering the concepts of the present invention.

As described previously, each embodiment has sixteen functionalrequirements (corresponding with the 16 rows of each operating modetable shown in the Figures) which may be grouped into five operatingmodes. The first operating mode is the “battery reverse mode” whichcorresponds with the first row (Batt Rev) of the operating mode table ofFIG. 2 b. In this mode, the engine is off and the transmission elementconnected to the engine is effectively allowed to freewheel, subject toengine inertia torque. The EVT is driven by one of the motor/generatorsusing energy from the battery, causing the vehicle to move in reverse.The other motor/generator may or may not rotate in this mode. As shownin FIG. 2 b, in this mode the clutch 150 is engaged and the dog clutch192 is in position B, the generator 180 has a torque of 0.90 units, themotor 182 has a torque of 0.30 units and an output torque of −8.33 isachieved, by way of example.

The second operating mode is the “EVT reverse mode” (or mechanicalreverse mode) which corresponds with the second row (EVT Rev) of theoperating mode table of FIG. 2 b. In this mode, the EVT is driven by theengine and by one of the motor/generators. The other motor/generatoroperates in generator mode and transfers 100% of the generated energyback to the driving motor. The net effect is to drive the vehicle inreverse. In this mode, the clutch 150 is engaged and the dog clutch 192is in position B, the motor 180 has a torque of −2.05 units, thegenerator 182 has a torque of −0.91 units, and an output torque of −8.33is achieved, corresponding to an input torque of 1 unit.

The third operating mode includes the “reverse and forward launch modes”corresponding with the third and fourth rows (TC Rev and TC For) of eachoperating mode table, such as that of FIG. 2 b. In this mode, the EVT isdriven by the engine and one of the motor/generators. A selectablefraction of the energy generated in the generator unit is stored in thebattery, with the remaining energy being transferred to the motor. In TCRev, the clutch 150 is engaged and the dog clutch 192 is in position B,the motor/generator 180 acts as a motor with −2.05 units of torque, themotor/generator 182 acts as a generator with −0.95 units of torque, anda torque ratio of −7.00 is achieved. In TC For, the clutch 150 isengaged and the dog clutch 192 is in position B, the motor/generator 180acts as a generator with 3.52 units of torque, the motor/generator 182acts as a motor with 0.52 units of torque, and a torque ratio of 5.00 isachieved. For these torque ratios, approximately 99% of the generatorenergy is stored in the battery.

The fourth operating mode includes the “Range 1.1, Range 1.2, Range 1.3,Range 1.4, Range 2.1, Range 3.1, Range 3.2 and Range 3.3” modescorresponding with rows 5-12 of the operating mode table of FIG. 2 b. Inthis mode, the EVT is driven by the engine as well as one of themotor/generators operating as a motor. The other motor/generatoroperates as a generator and transfers 100% of the generated energy backto the motor. The operating points represented by Range 1.1, 1.2, . . ., etc. are discrete points in the continuum of forward speed ratiosprovided by the EVT. For example in FIG. 2 b, a range of ratios from4.69 to 1.86 is achieved with the clutch 150 engaged and the dog clutch192 in position B. A ratio of 1.36 is achieved with the clutch 152engaged and the dog clutch 192 in position B. A range of ratios from1.00 to 0.54 is achieved with the clutch 152 engaged and the dog clutch192 in position A.

The fifth operating mode includes the fixed “ratio” modes (F1, F2, F3and F4) corresponding with rows 13-16 of the operating mode table ofFIG. 2 b. In this mode the transmission operates like a conventionalautomatic transmission, with one torque transmitting device engaged tocreate a discrete transmission ratio. In fixed ratio F1 the clutch 150and brake 155 are engaged and dog clutch 192 is in position B to achievea fixed ratio of 2.77. In fixed ratio F2, the clutch 152 and brake 155are engaged and dog clutch 192 is in position B to achieve a fixed ratioof 1.66. In fixed ratio F3, the clutches 150 and 152 are engaged and thedog clutch 192 is in position B to achieve a fixed ratio of 1.14. Infixed ratio F4, the clutch 152 and brake 157 are engaged and the dogclutch 192 is in position B to achieve a fixed ratio of 0.77.

As set forth above, the engagement schedule for the torque transmittingdevices is shown in the operating mode table and fixed ratio mode tableof FIG. 2 b. FIG. 2 b also provides an example of torque ratios that areavailable utilizing the ring gear/sun gear tooth ratios given by way ofexample in FIG. 2 b. The N_(R1)/N_(S1) value is the tooth ratio of theplanetary gear set 120; the N_(R2)/N_(S2) value is the tooth ratio ofthe planetary gear set 130; and the N_(R3)/N_(S3) value is the toothratio of the planetary gear set 140. Also, the chart of FIG. 2 bdescribes the ratio steps that are attained utilizing the sample oftooth ratios given. For example, the step ratio between first and secondfixed forward torque ratios is 1.67, and the ratio spread is 3.60.

Description of a Third Exemplary Embodiment

With reference to FIG. 3 a, a powertrain 210 is shown, including anengine 12 connected to another embodiment of the improved electricallyvariable transmission, designated generally by the numeral 214. Thetransmission 214 is designed to receive at least a portion of itsdriving power from the engine 12. As shown, the engine 12 has an outputshaft that serves as the input member 17 of the transmission 214. Atransient torque damper (not shown) may also be implemented between theengine 12 and the input member 17 of the transmission 214.

Irrespective of the means by which the engine 12 is connected to thetransmission input member 17, the transmission input member isoperatively connected to a planetary gear set in the transmission 214.An output member 19 of the transmission 214 is connected to a finaldrive 16.

The transmission 214 utilizes three differential gear sets, preferablyin the nature of planetary gear sets 220, 230 and 240. The planetarygear set 220 employs an outer gear member 224, typically designated asthe ring gear. The ring gear member 224 circumscribes an inner gearmember 222, typically designated as the sun gear. A carrier member 226rotatably supports a plurality of planet gears 227 such that each planetgear 227 meshingly engages both the outer, ring gear member 224 and theinner, sun gear member 222 of the first planetary gear set 220.

The planetary gear set 230 also has an outer ring gear member 234 thatcircumscribes an inner sun gear member 232. A plurality of planet gears237 are also rotatably mounted in a carrier member 236 such that eachplanet gear 237 simultaneously, and meshingly, engages both the outerring gear member 234 and the inner sun gear member 232 of the planetarygear set 230.

The planetary gear set 240 also has an outer ring gear member 244 thatcircumscribes an inner sun gear member 242. A plurality of planet gears247, 248 are rotatably mounted in a carrier member 246 such that eachplanet gear member 247 engages the inner, sun gear member 242 and theplanet gear members 248 simultaneously and meshingly engage both theouter, ring gear member 244 and the respective planet gear 247 of theplanetary gear set 240.

The transmission input member 17 is connected to the ring gear member224. The transmission output member 19 is connected to the ring gearmember 244. A first interconnecting member 270 continuously connects thesun gear member 222 with the ring gear member 234. A secondinterconnecting member 272 continuously connects the sun gear member 222with the sun gear member 242. A third interconnecting member 274continuously connects the carrier member 226 with the carrier member236.

The transmission 214 also incorporates first and second motor/generators280 and 282, respectively. The stator of the first motor/generator 280is secured to the transmission housing 260. The rotor of the firstmotor/generator 280 is secured to the carrier member 226.

The stator of the second motor/generator 282 is also secured to thetransmission housing 260. The rotor of the second motor/generator 282 isselectively connectable to the ring gear member 244 or the sun gearmember 232 via the dog clutch 292 alternating between positions “A” and“B”. The rotor of the second motor/generator 282 is connected to the dogclutch 292 via offset gearing 290. The dog clutch may be replaced by apair of clutches as is understood by those skilled in the art.

A first torque transmitting device, such as clutch 250, selectivelyconnects the carrier member 226 with the ring gear member 224. A secondtorque transmitting device, such as clutch 252, selectively connects thesun gear member 232 with the carrier member 246. A third torquetransmitting device, such as a brake 254, selectively connects thecarrier member 246 with the transmission housing 260. A fourth torquetransmitting device, such as the brake 255, is connected in parallelwith the motor/generator 280 for selectively braking rotation thereof. Afifth torque transmitting device, such as brake 257, is connected inparallel with the motor/generator 282 for selectively braking rotationthereof. The first, second, third, fourth and fifth torque transmittingdevices 250, 252, 254, 255 and 257 are employed to assist in theselection of the operational modes of the hybrid transmission 214.

The hybrid transmission 214 receives power from the engine 12, and alsofrom electric power source 286, which is operably connected to acontroller 288.

The operating mode table of FIG. 3 b illustrates the clutchingengagements, motor/generator conditions and output/input ratios for thefive operating modes of the transmission 214. These modes include the“battery reverse mode” (Batt Rev), “EVT reverse mode” (EVT Rev),“reverse and forward launch modes” (TC Rev and TC For), “range 1.1, 1.2,1.3 . . . modes” and “fixed ratio modes” (F1, F2, F3 and F4) asdescribed previously.

As set forth above the engagement schedule for the torque transmittingdevices is shown in the operating mode table and fixed ratio mode tableof FIG. 3 b. FIG. 3 b also provides an example of torque ratios that areavailable utilizing the ring gear/sun gear tooth ratios given by way ofexample in FIG. 3 b. The N_(R1)/N_(S1) value is the tooth ratio of theplanetary gear set 220; the N_(R2)/N_(S2) value is the tooth ratio ofthe planetary gear set 230; and the N_(R3)/N_(S3) value is the toothratio of the planetary gear set 240. Also, the chart of FIG. 3 bdescribes the ratio steps that are attained utilizing the sample oftooth ratios given. For example, the step ratio between the first andsecond fixed forward torque ratios is 1.73, and the ratio spread is4.73.

Description of a Fourth Exemplary Embodiment

With reference to FIG. 4 a, a powertrain 310 is shown, including anengine 12 connected to another embodiment of the improved electricallyvariable transmission, designated generally by the numeral 314. Thetransmission 314 is designed to receive at least a portion of itsdriving power from the engine 12.

As shown, the engine 12 has an output shaft that serves as the inputmember 17 of the transmission 314. A transient torque damper (not shown)may also be implemented between the engine 12 and the input member 17 ofthe transmission.

Irrespective of the means by which the engine 12 is connected to thetransmission input member 17, the transmission input member 17 isoperatively connected to a planetary gear set in the transmission 314.An output member 19 of the transmission 314 is connected to a finaldrive 16.

The transmission 314 utilizes three planetary gear sets 320, 330 and340. The planetary gear set 320 employs an outer ring gear member 324which circumscribes an inner sun gear member 322. A carrier member 326rotatably supports a plurality of planet gears 327 such that each planetgear 327 meshingly engages both the outer ring gear member 324 and theinner sun gear member 322 of the first planetary gear set 320.

The planetary gear set 330 also has an outer ring gear member 334 thatcircumscribes an inner sun gear member 332. A plurality of planet gears337 are also rotatably mounted in a carrier member 336 such that eachplanet gear member 337 simultaneously, and meshingly engages both theouter, ring gear member 334 and the inner, sun gear member 332 of theplanetary gear set 330.

The planetary gear set 340 also has an outer ring gear member 344 thatcircumscribes an inner sun gear member 342. A plurality of planet gears347 are also rotatably mounted in a carrier member 346 such that eachplanet gear member 347 simultaneously, and meshingly, engages both theouter ring gear member 344 and the inner sun gear member 342 of theplanetary gear set 340.

The transmission input member 17 is connected with the carrier member326. The transmission output member 19 is connected with the carriermember 336. A first interconnecting member 370 continuously connectscarrier member 326 with the ring gear member 334. A secondinterconnecting member 372 continuously connects the ring gear member324 with the ring gear member 344. A third interconnecting member 374continuously connects the sun gear member 332 with the sun gear member342.

The transmission 314 also incorporates first and second motor/generators380 and 382, respectively. The stator of the first motor/generator 380is secured to the transmission housing 360. The rotor of the firstmotor/generator 380 is secured to the sun gear member 322.

The stator of the second motor/generator 382 is also secured to thetransmission housing 360. The rotor of the second motor/generator 382 isselectively connectable to the carrier member 336 or the sun gear member342 via the dog clutch 392 alternating between positions “A” and “B”.The rotor of the second motor/generator 382 is connected to the dogclutch 392 via offset gearing 390. The dog clutch may be replaced by apair of clutches as is understood by those skilled in the art.

A first torque transmitting device, such as clutch 350, selectivelyconnects the ring gear member 324 with the carrier member 336. A secondtorque transmitting device, such as clutch 352, selectively connects thesun gear member 342 with the ring gear member 344. A third torquetransmitting device, such as brake 354, selectively connects the carriermember 346 with the transmission housing 360. A fourth torquetransmitting device, such as the brake 355, is connected in parallelwith the motor/generator 380 for selectively braking rotation thereof. Afifth torque transmitting device, such as the brake 357, is connected inparallel with the motor/generator 382 for selectively braking rotationthereof. The first, second, third, fourth and fifth torque transmittingdevices 350, 352, 354, 355 and 357 are employed to assist in theselection of the operational modes of the transmission 314.

The hybrid transmission 314 receives power from the engine 12, and alsoexchanges power with an electric power source 386, which is operablyconnected to a controller 388.

The operating mode table of FIG. 4 b illustrates the clutchingengagements, motor/generator conditions and output/input ratios for thefive operating modes of the transmission 314. These modes include the“battery reverse mode” (Batt Rev), the “EVT reverse mode” (EVT Rev),“reverse and forward launch modes” (TC Rev and TC For), “continuouslyvariable transmission range modes” (Range 1.1, 1.2, 1.3 . . . ) and“fixed ratio modes” (F1, F2, F3 and F4) as described previously.

As set forth above, the engagement schedule for the torque transmittingdevices is shown in the operating mode table and fixed ratio mode tableof FIG. 4 b. FIG. 4 b also provides an example of torque ratios that areavailable utilizing the ring gear/sun gear tooth ratios given by way ofexample in FIG. 4 b. The N_(R1)/N_(S1) value is the tooth ratio of theplanetary gear set 320; the N_(R2)/N_(S2) value is the tooth ratio ofthe planetary gear set 330; and the N_(R3)/N_(S3) value is the toothratio of the planetary gear set 340. Also, the chart of FIG. 4 bdescribes the ratio steps that are attained utilizing the sample oftooth ratios given. For example, the step ratio between first and secondfixed forward torque ratios is 1.77, and the ratio spread is 4.48.

Description of a Fifth Exemplary Embodiment

With reference to FIG. 5 a, a powertrain 410 is shown, including anengine 12 connected to another embodiment of the improved electricallyvariable transmission, designated generally by the numeral 414. Thetransmission 414 is designed to receive at least a portion of itsdriving power from the engine 12.

As shown, the engine 12 has an output shaft that serves as the inputmember 17 of the transmission 414. A transient torque damper (not shown)may also be implemented between the engine 12 and the input member 17 ofthe transmission.

Irrespective of the means by which the engine 12 is connected to thetransmission input member 17, the transmission input member 17 isoperatively connected to a planetary gear set in the transmission 414.An output member 19 of the transmission 414 is connected to a finaldrive 16.

The transmission 414 utilizes three planetary gear sets 420, 430 and440. The planetary gear set 420 employs an outer ring gear member 424which circumscribes an inner sun gear member 422. A carrier member 426rotatably supports a plurality of planet gears 427 such that each planetgear 427 meshingly engages both the outer ring gear member 424 and theinner sun gear member 422 of the first planetary gear set 420.

The planetary gear set 430 also has an outer ring gear member 434 thatcircumscribes an inner sun gear member 432. A plurality of planet gears437 are also rotatably mounted in a carrier member 436 such that eachplanet gear member 437 simultaneously, and meshingly engages both theouter, ring gear member 434 and the inner, sun gear member 432 of theplanetary gear set 430.

The planetary gear set 440 also has an outer ring gear member 444 thatcircumscribes an inner sun gear member 442. A plurality of planet gears447 are also rotatably mounted in a carrier member 446 such that eachplanet gear member 447 simultaneously, and meshingly, engages both theouter ring gear member 444 and the inner sun gear member 442 of theplanetary gear set 440.

The transmission input member 17 is continuously connected with the ringgear member 424. The transmission output member 19 is continuouslyconnected with the ring gear member 444. A first interconnecting member470 continuously connects the carrier member 426 with the ring gearmember 434. A second interconnecting member 472 continuously connectsthe sun gear member 422 with the transmission housing 460. A thirdinterconnecting member 474 continuously connects the carrier member 436with the carrier member 446.

The transmission 414 also incorporates first and second motor/generators480 and 482, respectively. The stator of the first motor/generator 480is secured to the transmission housing 460. The rotor of the firstmotor/generator 480 is secured to the carrier member 426.

The stator of the second motor/generator 482 is also secured to thetransmission housing 460. The rotor of the second motor/generator 482 isselectively alternately connectable to the ring gear member 444 or thesun gear member 442 via the dog clutch 492 alternating between positions“A” and “B”. The rotor of the second motor/generator 482 is connected tothe dog clutch 492 via offset gearing 490. The dog clutch may bereplaced by a pair of clutches as is understood by those skilled in theart.

A first torque transmitting device, such as clutch 450, selectivelyconnects the ring gear member 424 with the carrier member 436. A secondtorque transmitting device, such as clutch 452, selectively connects thesun gear member 432 with the sun gear member 442. A third torquetransmitting device, such as brake 454, selectively connects the carriermember 436 with the transmission housing 460. A fourth torquetransmitting device, such as the brake 457, is connected in parallelwith the motor/generator 482 for selectively braking rotation thereofThe first, second, third and fourth torque transmitting devices 450,452, 454 and 457 are employed to assist in the selection of theoperational modes of the transmission 414. The hybrid transmission 414receives power from the engine 12 and also from an electric power source486, which is operably connected to a controller 488.

The operating mode table of FIG. 5 b illustrates the clutchingengagements, motor/generator conditions and output/input ratios for thefive operating modes of the transmission 414. These modes include the“battery reverse mode” (Batt Rev), the “EVT reverse mode” (EVT Rev),“reverse and forward launch modes” (TC Rev and TC For), “continuouslyvariable transmission range modes” (Range 1.1, 1.2, 1.3 . . . ) and“fixed ratio modes” (F1, F2, F3 and F4) as described previously.

As set forth above, the engagement schedule for the torque transmittingdevices is shown in the operating mode table and fixed ratio mode tableof FIG. 5 b. FIG. 5 b also provides an example of torque ratios that areavailable utilizing the ring gear/sun gear tooth ratios given by way ofexample in FIG. 5 b. The N_(R1)/N_(S1) value is the tooth ratio of theplanetary gear set 420; the N_(R2)/N_(S2) value is the tooth ratio ofthe planetary gear set 430; and the N_(R3)/N_(S3) value is the toothratio of the planetary gear set 440. Also, the chart of FIG. 5 bdescribes the ratio steps that are attained utilizing the sample oftooth ratios given. For example, the step ratio between first and secondfixed forward torque ratios is 1.58, and the ratio spread is 3.97.

In the claims, the language “continuously connected” or “continuouslyconnecting” refers to a direct connection or a proportionally gearedconnection, such as gearing to an offset axis. Also, the “stationarymember” or “ground” may include the transmission housing (case) or anyother non-rotating component or components. Also, when a torquetransmitting mechanism is said to connect something to a member of agear set, it may also be connected to an interconnecting member whichconnects it with that member. It is further understood that differentfeatures from different embodiments of the invention may be combinedwithin the scope of the appended claims.

While various preferred embodiments of the present invention aredisclosed, it is to be understood that the concepts of the presentinvention are susceptible to numerous changes apparent to one skilled inthe art. Therefore, the scope of the present invention is not to belimited to the details shown and described but is intended to includeall variations and modifications which come within the scope of theappended claims.

1. An electrically variable transmission comprising: an input member toreceive power from an engine; an output member; first and secondmotor/generators; first, second and third differential gear sets eachhaving first, second and third members; said input member beingcontinuously connected with at least one member of said gear sets, andsaid output member being continuously connected with another member ofsaid gear sets; a first interconnecting member continuously connectingsaid first member of said first gear set with said first member of saidsecond gear set; a second interconnecting member continuously connectingsaid first member of said third gear set with said second or thirdmember of said first gear set or with a a stationary member; a thirdinterconnecting member continuously connecting said second member ofsaid first gear set with said second member of said second or third gearset; said first motor/generator being continuously connected with amember of said first or second gear set; said second motor/generatorbeing selectively connected via a dog clutch with members of said first,second or third gear sets; a first torque transmitting deviceselectively connecting a member of said first gear set to another memberof said first, second or third gear set; a second torque transmittingdevice selectively connecting a member of said third gear set with amember of said first or second gear set; a third torque transmittingdevice connected in parallel with the one of said first and secondmotor/generators for selectively preventing rotation thereof; a fourthtorque tramsmitting device selectively connecting a member of said thirdgear set with said stationary member; and wherein said first, second,third and fourth torque transmitting devices are engagable to provide anelectrically variable transmission with a continuously variable range ofspeed ratios and four fixed forward speed ratios.
 2. The electricallyvariable transmission of claim 1, wherein said first, second and thirddifferential gear sets are planetary gear sets.
 3. The electricallyvariable transmission of claim 2, wherein carrier members of each ofsaid planetary gear sets are single-pinion carrier members.
 4. Theelectrically variable transmission of claim 2, wherein at least onecarrier member of said planetary gear sets is a double-pinion carriermember.
 5. The electrically variable transmission of claim 1, whereinsaid first, second, third and fourth torque transmitting devices andsaid first and second motor/generators are operable to provide fiveoperating modes in the electrically variable transmission, includingbattery reverse mode, EVT reverse mode, reverse and forward launchmodes, continuously variable transmission range mode, and fixed ratiomode.
 6. The electrically variable transmission of claim 1, furthercomprising: a fifth torque transmitting device connected in parallelwith the other of said first and second motor/generators for selectivelypreventing rotation thereof; and wherein said first, second, third,fourth and fifth torque transmitting devices and said first and secondmotor/generators are operable to provide five operating modes in theelectrically variable transmission, including battery reverse mode, EVTreverse mode, reverse and forward launch modes, continuously variabletransmission range mode, and fixed ratio mode.
 7. An electricallyvariable transmission comprising: an input member to receive power froman engine; an output member; first and second motor/generators; first,second and third differential gear sets each having first, second andthird members; said input member being continuously connected with atleast one member of said gear sets, and said output member beingcontinuously connected with another member of said gear sets; a firstinterconnecting member continuously connecting said first member of saidfirst gear set with said first member of said second gear set; a secondinterconnecting member continuously connecting said first member of saidthird gear set with said second or third member of said first gear set,or with a stationary member; a third interconnecting member continuouslyconnecting said second member of said first gear set with said secondmember of said second or third gear set; said first motor/generatorbeing continuously connected with a member of said first or second gearset; said second motor/generator being selectively connected via a dogclutch with members of said first, second or third gear sets; first,second, third and fourth torque transmitting devices for selectivelyconnecting said members of said first, second or third gear sets with astationary member or with other members of said gear sets, said first,second, third and fourth torque transmitting devices being engagable toprovide an electrically variable transmission with a continuouslyvariable range of speed ratios and four fixed forward speed ratiosbetween said input member and said output member; and wherein saidfourth torque transmitting device selectively connects a member of saidthird gear set with said stationary member.
 8. The electrically variabletransmission of claim 7, wherein said first, second and thirddifferential gear sets are planetary gear sets, and said first torquetransmitting device selectively connects a member of said first gear setwith another member of said first, second or third gear set.
 9. Theelectrically variable transmission of claim 8, wherein said secondtorque transmitting device selectively connects a member of said thirdgear set with a member of said first or second gear set.
 10. Theelectrically variable transmission of claim 9, wherein said third torquetransmitting device is connected in parallel with one of saidmotor/generators for selectively preventing rotation thereof.
 11. Theelectrically variable transmission of claim 10, further comprising: afifth torque transmitting device connected in parallel with the other ofsaid motor/generators for selectively preventing rotation thereof. 12.The electrically variable transmission of claim 8, wherein carriermembers of each of said planetary gear sets are single-pinion carriermembers
 13. The electrically variable transmission of claim 8, whereinat least one carrier member of said planetary gear sets is adouble-pinion carrier member.
 14. An electrically variable transmissioncomprising an input member to receive power from am engine; an outputmember; first and second motor/generators; first, second and thirddifferential gear sets each having first, second and third members; saidinput member being continuously connected with at least one member ofsaid gear sets, and said output member being continuously connected withanother member of said gear sets; a first interconnecting membercontinuously connecting said first member of said first gear set withsaid first member of said second gear set; a second interconnectingmember continuously connecting said first member of said third gear setwith said second or third member of said first gear set or with astationary member; a third interconnecting member continuouslyconnecting said second member of said first gear set with said secondmember of said second or third gear set; said first motor/generatorbeing continuously connected with a member of said first or second gearset; said second motor/generator being selectively connected via a dogclutch with members of said first, second of third gear sets; a firsttorque transmitting device selectively connecting a member of said firstgear set to another member of said first, second or third gear set; asecond torque transmitting device selectively connecting a member ofsaid third gear set with a member of said first or second gear set; athird torque transmitting device connected in parallel with one of saidfirst and second motor/generators for selectively preventing rotationthereof; a fourth torque transmitting device selectively connecting amember of said third gear set with said stationary member; a fifthtorque transmitting device connected in parallel with the other one ofsaid first and second motor/generators for selectively preventingrotation thereof; and wherein said first, second, third, fourth andfifth torque transmitting devices are engagable to provide anelectrically variable transmission with a continuously variable range ofspeed ratios and four fixed forward speed ratios.